Lymphokines facilitate maturation of oligodendrocytes in vitro

Nexilin Regulates Oligodendrocyte Progenitor Cell Migration and Remyelination and Is Negatively Regulated by Protease-Activated Receptor 1/Ras-Proximate-1 Signaling Following Subarachnoid Hemorrhage

Progressive white matter (WM) impairments caused by subarachnoid hemorrhage (SAH) contribute to cognitive deficits and poor clinical prognoses; however, their pathogenetic mechanisms are poorly understood. We investigated the role of nexilin and oligodendrocyte progenitor cell (OPC)-mediated repair in a mouse model of experimental SAH generated via left endovascular perforation. Nexilin expression was enhanced by the elevated migration of OPCs after SAH. Knocking down nexilin by siRNA reduced OPC migration both in vitro and in vivo and abridged WM repair. In contrast, the protease-activated receptor 1 (PAR1), Ras-proximate-1 (RAP1) and phosphorylated RAP1 (pRAP1) levels in WM were elevated after SAH. The genetic inhibition of PAR1 reduced RAP1 and pRAP1 expression, further enhancing nexilin expression. When delivered at an early stage at a concentration of 25 µg/kg, thrombin receptor antagonist peptide along with PAR1 knockdown rescued the down-regulation of myelin basic protein and improved remyelination at the later stage of SAH. Our results suggest that nexilin is required for OPC migration and remyelination following SAH, as it negatively regulates PAR1/RAP1 signaling, thus providing a promising therapeutic target in WM repair and functional recovery.

The adult rat hippocampus contains primordial neural stem cells

Adult-derived hippocampal progenitors generate neurons, astrocytes, and oligodendrocytes in vitro and following grafting into the adult brain. Although these progenitors have a considerable capacity for in vitro self renewal, it is not known if each lineage is generated by separate committed precursors or by multipotent stem cells. By genetic marking, we have followed individual cells through the process of proliferative expansion, commitment, and differentiation. All three lineages are generated by single marked cells and the relative proportions of each lineage can be strongly influenced by environmental cues. Differentiation is accompanied by a characteristic progression of lineage-specific markers and can be potentiated by retinoic acid, elevated cyclic AMP, or neurotrophic factors. The ability to genetically mark and clone normal diploid hippocampal progenitors provides the first definitive evidence that multipotent neural stem cells exist outside of the adult striatal subventricular zone and supports the hypothesis that FGF-2-responsive neural stem cells may be broadly distributed in the adult brain.

Glial development in primary cultures established from normal and X-irradiated neonatal spinal cord

The glial population of the lumbosacral spinal cord of the rat can be markedly depleted by exposure to ionizing radiation during the first postnatal week. Identification of specific cell populations which survive the exposure to radiation is difficult in situ; therefore, the present investigation used in vitro approaches to address issues related to specific phenotypes and maturational states of glia in cultures derived from non-irradiated (control) and irradiated (experimental) lumbosacral spinal cords of 3-day-old rats. Cultures were established from the spinal cords 2 to 4 hours following irradiation and were compared to cultures from non-irradiated, littermate controls. By 4 days in vitro (DIV) the numbers of cells in experimental cultures were profoundly reduced when compared to controls, and this reduction persisted through the termination of the study (8 DIV). In addition to reduction in numbers, astrocyte phenotypes were altered in experimental cultures, with greater proportions of the astrocyte population being constituted by the flat angular, large angular, and pancake types and a lesser proportion by stellate cells. The non-astrocytic cell types were dramatically reduced as evidenced by the paucity of oligodendrocytes immunoreactive for galactocerebroside and of small, non-process bearing cells binding the lectin, Griffonia (Bandeiraea) simplicifolia, a marker for microglia. Experimental cultures contained an increased incidence of binucleate astrocytes, an increase not restricted to a particular astrocyte phenotype. This study established the feasibility of utilizing this combined in vivo/in vitro approach in assessment of glial populations in immature spinal cords, and further investigations are in progress using this model.

Tumor necrosis factor inhibits K+ current expression in cultured oligodendrocytes

The effects of tumor necrosis factor-alpha (TNF-alpha), a cytokine secreted by activated macrophages, on the electrical membrane properties of cultured adult ovine oligodendrocytes (OLGs) were investigated using the whole-cell voltage-clamp technique. Treatment with recombinant human TNF-alpha (rhTNF) for 24 to 72 hr produces (i) process retraction in some but not all OLGs, (ii) a reduction in the resting membrane potential with no significant change in membrane capacitance or input resistance over control cells and (iii) a decrease in the expression of both the inwardly rectifying and outward K+ current. The magnitude of the membrane potential change as well as K+ current inhibition was larger in cells with retracted processes. The electrophysiological effects of rhTNF were attenuated when rhTNF was neutralized with a polyclonal anti-rhTNF antibody. The binding of rhTNF to its receptor has been reported to increase GTP binding, to increase GTPase activity of a pertussis-sensitive G protein, and to produce an elevation in intracellular cAMP in other cell types. However, pretreatment of OLGs with activated pertussis toxin failed to attenuate or mimic the effects of rhTNF. Chronic exposure of OLGs to the membrane permeant analogue of cAMP, 8-bromo-cAMP, resulted primarily in an inhibition of the inwardly rectifying K+ current, an effect which was less than that produced by rhTNF alone and without any of the associated rhTNF-induced morphological changes. This indicates that the effects of rhTNF cannot be entirely accounted for by an elevation in intracellular cAMP. Cycloheximide (CHX), an inhibitor of protein synthesis, mimicked the effects of rhTNF; however, the effects of rhTNF and CHX were not additive. The finding that both ionic current expression and membrane potential were reduced in cells treated with rhTNF that appeared morphologically normal suggests that abnormal ion channel expression in OLGs precedes and may contribute to eventual myelin swelling and damage.

Growth factor responses of enriched bipotential glial progenitors

Responses of oligodendrocyte/type 2 astrocyte (O-2A) glial progenitors from neonatal rat brains to different growth factors were studied by a new, serum-free method. Enriched tertiary cultures of O-2A progenitors were produced after 6-7 days in vitro using the growth-promoting factors from the B104 CNS neuronal cell line, heparin, and mechanical separation. These cultures contained about 75-90% A2B5+ cells with less than 10% type 1 astrocytes, and the yield was 4.4 x 10(5) cells/brain. B104 conditioned medium (CM) factors increased both O-2A progenitor number and [3H]thymidine-labeling indices after three days. However, type 1 astrocyte CM was required for continued survival of enriched progenitors beyond 1 day in tertiary culture. Platelet-derived growth factor (PDGF) and glia maturation factor also showed growth-promoting action, but were less effective than B104 CM at tested doses. PDGF-neutralizing antibodies had no effect on progenitor survival or response to B104 CM factors. Thus, type 1 astrocyte-derived PDGF was not required for this response, B104 CM is not likely to contain PDGF, and B104 CM factors act directly on O-2A progenitors. Fibroblast growth factor, transforming growth factor beta, interleukin 2, epidermal growth factor, and triiodothyronine showed no growth-promoting activity; moreover, interleukin 2, epidermal growth factor, transforming growth factor beta, and 0.5% fetal bovine serum inhibited B104 CM action. Enriched progenitors exhibited bipotentiality by slowly differentiating into oligodendrocytes in serum-free medium, whereas culture in 10% fetal bovine serum increased type 2 astrocytes. Thus, this new method selects or produces progenitors which are similar to those from mature brains.